The present invention relates to an alkaline storage battery having a negative electrode comprising an AB5 type hydrogen storage alloy.
As a typical example of an alkaline storage battery having a negative electrode comprising a hydrogen storage alloy which can absorb and desorb hydrogen reversibly, there is a nickel-metal hydride storage battery having a positive electrode comprising nickel hydroxide. The nickel-metal hydride storage battery is widely used as a power source of portable instruments such as a cellular phone, personal computer, power tool and the like. Recently, as a main power source of an electric vehicle and the like, practical use of a nickel-metal hydride storage battery has been developed. Thus, a nickel-metal hydride storage battery is often used at high output. Therefore, further improvement in discharging property at a large current (high-rate discharging property) is required for a nickel-metal hydride storage battery.
However, an alkaline storage battery having a negative electrode comprising a hydrogen storage alloy has a problem that high-rate discharging property tends to be insufficient at the initial charging and discharging cycles.
Conventionally, the following improvements of negative electrodes have been tried.
Japanese Laid-Open Patent Sho 63-146353 suggests a method in which a hydrogen storage alloy powder is immersed in an aqueous alkaline solution having a specific gravity of 1.1 or more at temperatures in a range of 45 to 100xc2x0 C. for 0.2 to 24 hours. When a hydrogen storage alloy powder which had been subjected to such a treatment is used in a negative electrode, a discharging capacity obtained in a cycle of charging and discharging at the initial stage can be maintained even after the cycle is repeated 200 times or more.
Japanese Laid-Open Patent Hei 2-267872 suggests that it be effective to conduct a formation treatment at least once after assembly of a battery. The treatment has a process of charging the battery and a process of discharging the charged battery at a higher temperature than in the charging process. When such a formation treatment is performed, low-rate discharging property of a battery is increased.
Japanese Laid-Open Patent Hei 4-137361 suggests that metallic nickel and cobalt, and an oxide of at least one constituent element of a hydrogen storage alloy are allowed to exist in admixture on the surface of the hydrogen storage alloy. Such a surface condition of a hydrogen storage alloy is obtained, for example, by immersing a hydrogen storage alloy powder into an aqueous alkaline solution. For example, when metallic nickel and metallic cobalt in a total amount corresponding to a magnetization strength of 0.005 to 12 emu/g are contained in a hydrogen storage alloy, the increase of inner pressure of a battery due to generation of hydrogen gas is suppressed, leading to an improvement of cycle life of the battery.
Though any of the above-mentioned battery having a negative electrode comprising a hydrogen storage alloy is improved in cycle life or low-rate discharging property, a battery which can manifest an excellent high-rate discharging property at the initial charging and discharging cycles has not been provided.
The object of the present invention is to provide a high output alkaline storage battery which can manifest an excellent high-rate discharging property, particullarly at the initial charging and discharging cycles.
The present invention relates to an alkaline storage battery comprising a positive electrode, a negative electrode, and an alkaline electrolyte, said negative electrode comprising an AB5 type hydrogen storage alloy containing at least nickel as B element, wherein the hydrogen storage alloy contains 1.5 to 5.0% by weight, preferably 2.0 to 4.0% by weight of a magnetic substance comprising metallic nickel.
The hydrogen storage alloy preferably contains 45 to 55% by weight of nickel as B element.
It is preferable that the specific surface area of the hydrogen storage alloy is in a range of 0.2 to 5.0 m2/g, further 0.4 to 4.0 m2/g.
While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.